Lpg/petrol miss firing

Discussion in 'Tech/Mech General' started by MAUBRI, Feb 3, 2009.

  1. MAUBRI

    MAUBRI Funster

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    This is a strange one, I had a LPG conversion done in June last year. It works fine and has saved me quite a considerable amount since installation.

    However the conversion seems to have thrown up a problem in the Petrol department.
    ( Bearing in mind there was no problem before the conversion).

    I tried having a conversation with the Italian Convertor but he assures me that he did nothing to that side of things. So unless I can prove otherwise I am stuck.

    When I start up, its initialy on Petrol until such time the RV warms up, it then automatically changes over to LPG. During this warming up stage if I try moving off I get what seems to be miss firing ( It seems to be firng on 6 instead of 8). So I wait until its warm then move off on LPG(no problems).

    This is fine of course until I run out of LPG before the next fill up, when it changes back to petrol the miss firing starts all over again. This was a problem recently as I was negotiating Charmouth Hill towing Smarty. Anyone that knows that area of Dorset will know its a B at the best of times as it can be a standing start.

    I have checked the pump and its gushing well,I cant check the pump itself or even change it without a major upheaval as the LPG conversion feed pipes run under the Petrol tank, so I would need to be empty of LPG to dissconnect the pipe work.

    I have changed the Petrol filter.

    The firng system is the same on both systems so to me if LPG works so should the petrol.

    The last thing that I can think of is the timing, does anyone know how the system knows which fuel is being injected and how if at all the timing is altered if needs be.

    I know the LPG doesn't burn as efficiently as petrol , but does that mean the timing has to be altered.

    I am reluctant to go to a Specialist as I have always done my own work/maintenance until now I have not had a problem.

    The RV is a REXHALL VISION with a Ford 460 of 1997 vintage.

    Any ideas or persons to contact would be appreciated, was given one mobile mechanics number last week but still waiting for him to return my call.

    Brian
     
  2. Dodgey

    Dodgey Funster

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    Daft as it sounds, when did you last put petrol in, stuff goes off, less bang quite quickley....
     
  3. Terry

    Terry Funster

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    Hi, if it is running ok on gas then the problem is on the petrol side :thumb:It sounds like the choke is sticking on.If you look for the leccy bits to do the gas you should see a big fuse,pull this out and it cancels the gas side completely.Then you are left to figure out the petrol as normal.Once you have done this put the fuse back in and all will be hunky dory :thumb:It needs to run on petrol right to run on the gas right :thumb:
    terry
     
  4. American Dream

    American Dream Read Only Funster

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    Funnily enough Dodgey That is exactly what I was thinking.
     
  5. davejen

    davejen Funster

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    Hi, Brian, Ihad a similar problem with a Dodge dayvan I had converted a few years ago- ie it ran fine on petrol before the conversion but afterit wouldn't run properly . I had it back to the converter several times (round trip of about 80 miles) and he kept making small adjustments here and there but never completely solved the problem. I think partly due to the Italian instructions as I think they only went to 3.5 ltrs, so he was guessing about the settings for the bigger engine. Having said all that, he was recommended by a friend who had a Chevy dayvan done a while earlier. His system may have been different to the one on my van as it was done some time before mine.
    Anyway, on another subject , we spent 3 weeks at Cosawes Park quite near to Lanner and passed through the village a lot during our stay, and very nice it looks too. We were there over xmas/new year -never saw your RV though.
    Regards, Dave:thumb:
     
  6. Sundowners

    Sundowners Funster Life Member

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    do you know if a device was fitted to change the timeing when switching from one fuel to the other?? Is it carb. or fuel injection?
    Nigel
     
  7. American Dream

    American Dream Read Only Funster

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    I sometimes think they try to find a mid-point or "happy medium" between the 2 optimum ignition settings of LPG and Petrol.

    If you have true electronic ignition it would need 2 settings mapped in the ecu to run optimally.Can they do that?

    Does anyone know?
     
  8. MAUBRI

    MAUBRI Funster

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    Hi there thanks for your interest, thats the main problem the Italian Convertors English is a bit beyond me, if you know what i mean. Regarding device thats what I was hoping someone could tell me ? It's injection by the way

    Brian
     
  9. MAUBRI

    MAUBRI Funster

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    Hi Dave, you didn't say whether you ever cured the problem.
    Regards passing through Lanner, coming down the hill from Redruth direction , pass the Post Office, turn right up the hill and I'm up on the left overlooking the village,

    Cheers

    Brian
     
  10. American Dream

    American Dream Read Only Funster

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    Which comes back to the ecu mapping for timing the injectors.

    This suggests there are 2 ECU's in parallel. LPG Installations and Conversions: TARTARINI AUTO LPG SEQUENTIAL INJECTION SYSTEM which suggests it should be possible to map accurately for both fuels.

    LPG SEQUENTIAL SYSTEM [​IMG]The LPG SEQUENTIAL system is an electronically controlled gas feeding system that can be installed in all vehicles with sequential injection system. The system is a Multipoint sequential one and is controlled by an ecu that controls the gas injection sequence and the timing. The gas is injected through the rails of injectors directly into the suction pipes thus obtaining a particularly precise mix to optimise the combustion process. The gas injection timing is obtained by exploiting the petrol injection timing of the original cpu of the vehicle.This system offers the following benefits:

    1. Compatibility with vehicles equipped with OBD systems
    2. Optimisation of fuel consumption
    3. Reduction in exhaust pollution substances
    4. Optimisation of vehicle driving conditions
    5. Installation simplicity
    6. Auto-calibration with vehicle in neutral
    7. Auto-diagnosis
    8. Pre-arrangement for self-adaptation
    LPG SEQUENTIAL REGULATOR
    The LPG regulator-vaporizer is the single-stage type with diaphragm and is compensated by the vacuum of the suction manifold. It is designed to ensure a higher output pressure than the pressure inside the suction pipes of the engine. The engine coolant flows inside the regulator-vaporizer so that the LPG is completely vaporized. A solenoid valve complete with filter is fitted on the inlet of the regulator. A temperature sensor and a safety valve are fitted on the regulator casing.
    SEQUENTIAL ECU
    The SEQUENTIAL ecu is connected in parallel to the original petrol cpu. The petrol injection timing and engine rpm signals are processed by the sequential ecu and transformed into electric signals to command the injectors on the rails, thus optimising the driving conditions and fuel consumption levels of the vehicle. Once the vehicle has been converted, the installer simply connects a PC and executes the initial set-up of the basic parameters. If the dedicated map for the vehicle being converted is not available in the “data base”, the installer can still create the map for that vehicle simply by entering the parameters relative to the engine specifications. The ecu also offers other functions, such as: - It is pre-arranged for most level sensors sold in Italy and abroad. - It is pre-arranged to read all types of lambda probes. - It is pre-arranged to switch the system back to petrol automatically if there should be any anomalies in the system or if the gas runs out (the switch starts to buzz).- It is pre-arranged to analyse the anomalies recorded and to diagnose the ecu itself. -It records the time the vehicle runs on gas and records any possible anomalies encountered (these are reset when the vehicle is serviced).
    RAIL OF INJECTORS
    The rail sequentially dispenses the gas to each cylinder. This function is performed by separate and absolutely independent injectors, which receive the electric signal from the ecu. This signal enables the system to calibrate the amount of gas that is injected in just the cylinder in the suction phase and it also controls the cut-off function.
    SWITCH UNIT
    This very small electronic module is installed inside the vehicle compartment in a handy position for the driver. Thanks to its very small size it can be fitted in the place of an empty switch on the dashboard or a hole can be punched for it on the dashboard using a hot punch. The switch unit has the following functions: - It acts as a 2-position gas/petrol selector switch and indicates the fuel in use by means of two LED’s: A yellow one is lit when running on gas and a red one is lit when running on petrol. - It displays the amount of gas in the tank/cylinder by means of five LED’s: four green ones (1/4; 1/2; 3/4 and 4/4) and a red one for reserve. - It informs the driver on any anomalies encountered in the Etagas system by means of the red petrol LED that starts to flash.
     
    Last edited: Feb 3, 2009
  11. MAUBRI

    MAUBRI Funster

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    Hi Gents, regarding Old Petrol. I actualy 3/4 filled it at the end of the summer last year and I'm still at around 1/4 now.

    Brian
     
  12. Blisters

    Blisters Read Only Funster

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    Brian
    Having run gas cars for about 8 years I have had problems on both sides, usually a little service on the fuel side sorts it out, if your problem is on the petrol side replace the inline fuel filter and clean/replace all your spark plugs and reset the gaps, also gas burns hotter than petrol and dryer and i have had it miss fire on petrol did the above problem solved, is it worse when cold?
     
  13. American Dream

    American Dream Read Only Funster

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    Cheers for the info Brian.

    It was worth a thought.It's a strange thing..Old fuel.

    Smells ok but will it ignite properly!!!Got me going well and truly once.Stripped down and cleaned the fuel system and carbs and as a last resort drained and put new petrol in.:Doh:

    The B++++y thing started.:Blush:
     
  14. Dodgey

    Dodgey Funster

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    One would expect petrol to be OK over that duration but I have had this in that sort of time frame with the lawn mower, 'parked' over winter it wouldn't go just spluttered, topped up from 'it's' can still the same went and got fresh and vrooooom, splutter bang also as silencer has gone, but vroooom non the less.

    As per blister, service poss?

    Si.
     
  15. MAUBRI

    MAUBRI Funster

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    Hi, Thanks for your info, Have already changed filter but I think I will check plugs etc. in the next couple of days. reason for not doing so before was I was working on the logic that they worked ok with LPG.

    Brian
     
  16. MAUBRI

    MAUBRI Funster

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    Thanks for this Technical stuff, It makes me feel as though I am going to have to go back to the Convertor to find out what he did to my original Petrol setup and try and get it fixed, when the weather improves. Thanks again

    Brian
     
  17. MAUBRI

    MAUBRI Funster

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    Hi again,

    I am still at it. Went on a 500 mile round trip last weekend and found out a bit more. I had a mild overheating problem which was only evident when working MAUBRI hard which I assumed was due possibly to the misfiring when on petrol, but after having it on LPG as well I looked into it further half way through my trip.

    It seems that when the previous owner had the Altenator changed " someone" didn't tighten the adjuster bolt enough so it was gradually working loose thus the water pump was only just working. On my return leg the over heating problem had gone. The Petrol misfiring hadn't of course. When I returned home I checked the AUTOLITE 25 plugs and they were the correct colour and in peak condition, I was surprised that the gap was 42thou though, but I checked the book to be sure, all British and European vehicles I have had before have been 25 thou.
    My last thing I am going to have to change I think is the PETROL PUMP however that's virtualy impossible due to the plumbing route of the LPG being under the fuel tank. I have heard that its possible to connect a external pump and suck through the tank pump, however does any one know of what size/spec I would need i.e. flow rate etc.

    Cheers for looking
     
  18. ginge61

    ginge61 Read Only Funster

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    check for any air leaks and make sure all the joints on the exaust are tight as if they suck any air that may cause it if it was a fuel pump it would be missfireing on a few diff cylinders so check the plug leads to see which one is missfireing on or if its just missing on random ones and run some injector cleaner through it .i tend not to keep a lot of petrol in the tank as it will loose some of it octaine rateing over a few months on the timeing side of things it would be set to run on both so sounds more like a leek or injection prob
     
  19. davejen

    davejen Funster

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    Sorry, Brian the answer is unfortunately no they didn't completely cure it. Sorry for delay in answering your post.
    Regards, Dave:thumb:
     
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